Coating process using dense phase gas

Abstract

A process for coating a substrate with a chosen material comprising placing the substrate in a coating chamber and contacting the substrate with a mixture of the selected coating material in a chosen dense phase gas at a selected temperature and a pressure equal to or above the critical pressure of the dense phase gas for a period of time which is sufficient to allow complete penetration of the mixture into all surfaces of the substrate. Then, the phase of the dense phase gas is shifted to produce dissolution of the chosen material from the dense phase gas and to thereby form the coating of the chosen material on the substrate.

What is claimed is: 
     
       1. A method for forming a solid coating of a material on a substrate comprising the steps of: (a) providing a mixture of said material in gas or liquid form and a dense phase gas, wherein said material is capable of being dissolved in said dense phase gas, said dense phase gas having a critical temperature and a critical pressure;   (b) placing said substrate in said chamber with said mixture at a temperature ranging from 25K below said critical temperature to 100K above said critical temperature and a pressure equal to or above the critical pressure of said dense phase gas whereby said material becomes dissolved in said dense phase gas to form a solution, and maintaining said contacting for a period of time which is sufficient to allow complete penetration of said solution into all surfaces of said substrate; and   (d) shifting the phase of said dense phase gas from the supercritical state to the liquid state or from the liquid state to the supercritical state, whereby said material non-reactively precipitates out of said solution from said dense phase gas in said gas or liquid form and deposits in solid form on said substrate to form said coating on said substrate.   
     
     
       2. The method as set forth in claim 1 wherein said dense phase gas is shifted from the supercritical state to the liquid state. 
     
     
       3. The method as set forth in claim 2 wherein said shifting is provided by decreasing said temperature to a temperature below the critical temperature of said dense phase gas. 
     
     
       4. The method as set forth in claim 2 wherein said shifting is provided by decreasing said pressure to a pressure below said critical pressure of said dense phase gas. 
     
     
       5. The method as set forth in claim 1 wherein said dense phase gas is shifted from the liquid state to the supercritical state. 
     
     
       6. The method as set forth in claim 1 wherein said dense phase gas is selected from the group consisting of carbon dioxide, nitrous oxide, ammonia, helium, krypton, argon, methane, ethane, propane, butane, pentane, hexane, ethylene, propylene, tetrafluoromethane, chlorodifluoromethane, sulfur hexafluoride, perfluoropropane, and mixtures thereof. 
     
     
       7. The method as set forth in claim 1 wherein said coating is formed on the external surface of said substrate. 
     
     
       8. The method as set forth in claim 7 wherein said coating is exposed to ultraviolet radiation. 
     
     
       9. The method as set forth in claim 1 wherein said coating is formed on the interstitial surfaces of said substrate. 
     
     
       10. The method as set forth in claim 1 further comprising treating said coating to alter the properties thereof. 
     
     
       11. The method as set forth in claim 10 further comprising exposing said coating to a chosen reactant which reacts chemically with said coating to alter said coating.